1. Field of the Invention
The present invention relates to a reel driving mechanism for limiting the rotational torque for driving a reel table in an adaptive manner as well as a tape recorder having such a mechanism.
2. Description of the Related Art
Conventionally, when a tape is to be traveled in a reverse direction, a tape recorder is provided, on the side of a take-up reel, with a mechanism for applying brakes to a reel table since it is necessary to apply a certain degree of tension to the tape. In addition, this mechanism is so arranged to release the brakes when the tape is run in a forward direction, since the mechanism applies load to the take-up reel being driven.
FIG. 1 is a schematic top plan view of the take-up reel driving mechanism in a conventional video tape-recorder. This reel driving mechanism comprises the following component parts: a reel shaft 19; a reel table 20; a gear 21 for rotating the reel table 20 via a slip member such as felt (not shown); a brake claw 22 for fixing the gear 21, as necessary; a rotary shaft 23 of the brake claw 22; a spring 24 for urging the brake claw 22 counterclockwise; and a mode lever 25 for controlling the turn of the brake claw 22.
In the mechanism shown in FIG. 1, the brake torque at the time of running the tape in the reverse direction is set to substantially the same level as that of the take-up torque at the time when the tape is run in the forward direction. Namely, as the brake claw 22 is turned by the movement of the mode lever 25, a distal end portion 22a of the brake claw 22 is brought into contact with the reel gear 21 which is arranged to impart fixed torque to the reel table 20 when the tape is run in the forward direction. Consequently, this brake claw 22 stops the reel gear 21 when the tape is run in the reverse direction, thereby allowing fixed torque to be obtained. This is a frequently adopted system.
Also, there is another system in which braking torque for back tension is constantly applied to the take-up reel table.
As described above, in the conventional system in which the brake claw is operated by the movement of the mode lever, the mode lever has to be moved. Therefore, there have been drawbacks in that the use of the mode lever itself and driving mechanism therefor results in the tendency of the apparatus becoming large in size, higher costs, and larger weight, and that time is required for moving the mode lever during a changeover of the tape traveling direction, thereby making it impossible to effect a speedy changeover of the aforementioned traveling directions.
In addition, in the system in which the braking torque for back tension is constantly applied to the reel table, the above-described drawbacks are not present. However, since braking torque for back tension acts when the tape is run in the forward direction, there has been a problem in that the loss of the reel driving force is large.